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Why Can't We Remember Our Dreams?

Perhaps you've heard that the average person dreams four to six times each night. But did you know that most of us are unable to recall 90% of our dreams?

Today on A Moment of Science we ask why it is that we forget most of our dreams.

First, think about what happens when you fall asleep: one of the last regions of your brain to go into sleep mode is the hippocampus, a structure that plays a critical role in transferring information from short-term memory to long-term memory.

Of course, the hippocampus keeps working. It mostly consolidates information from the day. And waking up signals the hippocampus to start encoding new experiences in memory.

But that takes about two minutes, which is longer than most sleepers stay awake if they're roused in the night. In addition, most people are unable to retain their short-term memories of dreams after waking in the morning before the hippocampus reactivates.

People who wake up more often during sleep tend to stay awake for at least two minutes, which activates the hippocampus and gives them better recall of their dreams.

Besides the hardwiring in our brains, two neurotransmitters, acetylcholine and noradrenaline, also help us retain memories. Both of these neurotransmitters drop dramatically during sleep.

That combination keeps our brains working rapidly, without using any brain-power to actually save our dream memories.

Even our talk here about dreams could be a potent factor. Studies find that discussing or reading about dreams boosts short-term recall, while people who come to believe that dreams are valuable have better recall in the long term.

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